Fix selection of EPUB unique identifier (#85)

Author: qnga

readium/streamer/src/main/java/org/readium/r2/streamer/parser/epub/Metadata.kt

@@ -196,10 +196,11 @@ internal class PubMetadataAdapter(
     val identifier: String?
 
     init {
-        val identifiers = items[Vocabularies.DCTERMS + "identifier"]
-            ?.associate { Pair(it.property, it.value) }.orEmpty()
+        val identifiers = items[Vocabularies.DCTERMS + "identifier"].orEmpty()
 
-        identifier = uniqueIdentifierId?.let { identifiers[it] } ?: identifiers.values.firstOrNull()
+        identifier = uniqueIdentifierId
+            ?.let { uniqueId -> identifiers.firstOrNull { it.id == uniqueId }?.value }
+            ?: identifiers.firstOrNull()?.value
     }
 
     val published = firstValue(Vocabularies.DCTERMS + "date")?.iso8601ToDate()

readium/streamer/src/test/resources/org/readium/r2/streamer/parser/epub/package/identifier-unique.opf

@@ -3,8 +3,9 @@
   <metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
     <dc:title>Alice's Adventures in Wonderland</dc:title> 
     <dc:identifier> </dc:identifier>
-    <dc:identifier id="isbn">978-3-16-148410-0</dc:identifier>
+    <dc:identifier>BEQ</dc:identifier>
     <dc:identifier id="pub-id">urn:uuid:2</dc:identifier>
+    <dc:identifier id="isbn">978-3-16-148410-0</dc:identifier>
   </metadata>
   <manifest>
     <item id="titlepage" href="titlepage.xhtml" media-type="application/xhtml+xml" />